When tertiary butyl hydroperoxide is reacted with propylene to form propylene oxide, tertiary butyl alcohol is the main byproduct. The tertiary butyl alcohol is usually separated from the propylene oxide by distillation, but it will contain peroxide impurities such as tertiary butyl hydroperoxide and di-tertiary butyl peroxide. The tertiary butyl alcohol may be used as a gasoline additive, or it may be dehydrated to make isobutylene which can then be used to make methyl-t-butyl ether. The process of making isobutylene from tertiary butyl alcohol involves the use of a dehydration catalyst which is usually a metal ion which has been exchanged onto a resin support. However, the peroxides which are present in the tertiary butyl alcohol can destroy the dehydration catalyst and therefore it is necessary to reduce the amount of peroxide impurities to a few ppm, i.e., less than 20 ppm.
The prior art has addressed the problem of decomposition of peroxides in tertiary butyl alcohol in regard to use of tertiary butyl alcohol as a gasoline additive. For example, U.S. Pat. No. 3,474,151 discloses a process for decomposing peroxides in tertiary butyl alcohol by heating the tertiary butyl alcohol at a temperature of 375.degree. F. to 475.degree. F. Other references disclose catalytic methods for decomposing peroxide impurities in tertiary butyl alcohol feedstocks. These references include the following: 1) U.S. Pat. No. 4,551,553 which discloses a homogeneous process of decomposing hydroperoxides using a catalyst which is a chromium and ruthenium salt; 2) U.S. Pat. No. 4,873,380 which discloses the use of a catalyst which contains oxides of nickel, copper, chromium and barium to decompose tertiary butyl hydroperoxide and di-tertiary butyl peroxide in a tertiary butyl alcohol feedstock; 3) U.S. Pat. No. 4,742,179 which discloses the decomposition of peroxides in a tertiary butyl alcohol feedstock using a catalyst which consists of one or more of a group VIB or VIII metal which has been base treated and optionally contains a Group IB promoter; 4) U.S. Pat. No. 4,705,903 which discloses the decomposition of peroxides using a catalyst composed of iron, copper, chromia and cobalt; 5) U.S. Pat. No. 4,704,482 which discloses the decomposition of peroxides using a catalyst containing nickel, copper, chromia and iron oxide either unsupported or supported on silica; and 6) U.S. Pat. No. 4,547,598 which discloses a method of decomposing hydroperoxides using a catalyst which is cobalt borate or cobalt borate on titanium dioxide.
In contrast to this prior art, the instant invention reduces or decomposes tertiary butyl hydroperoxide and di-tertiary butyl peroxides to alcohols using an iron (II) compound. During the reaction the iron (II) is oxidized to iron (III) while the peroxides are reduced to the alcohol. The iron (II) compound may be used in a homogeneous phase, that is by using an iron (II) compound which is soluble in the tertiary butyl alcohol or by depositing the iron (II) compound onto a solid support such as a resin or a zeolite. By using only an iron (II) compound, applicants have been able to produce a tertiary butyl alcohol product that contains about 20 ppm of total peroxides. There is nothing in the prior art that suggests that iron (II) could be effective in decomposing tertiary butyl hydroperoxide and especially di-tertiary butyl peroxide which is difficult to decompose. Accordingly, applicants have met a need in the industry for a tertiary butyl alcohol feedstock which contains less than 20 ppm of total peroxide impurities so that the tertiary butyl alcohol may be dehydrated and then used to make methyl-t-butyl ether.
What is also surprising about applicants' invention is that the iron (II) compound is able to reduce the di-tertiary butyl peroxide. It is well known that di-tertiary butyl peroxide is one of the hardest peroxides to decompose and thus it is extremely surprising that an iron (II) compound can effectively and virtually completely reduce or decompose all the di-tertiary butyl peroxides contained in the tertiary butyl alcohol feedstock.